When video is shot under an environment illuminated with a (non-inverter) fluorescent lamp, the luminance signal varies due to the AC voltage frequency of the fluorescent lamp (at 50 Hz or 60 Hz), thus producing bright and dark portions in an image shot. Such a phenomenon is generally called “flicker”. In the field of such a flicker reducing technique, the techniques disclosed in Patent Documents Nos. 1 and 2 are known, for example.
According to the technique disclosed in Patent Document No. 1, as many values of a line integral as the number of frames corresponding to the greatest common divisor of the flicker period and frame period are stored in a memory. In this case, each of the values of the line integral is obtained by calculating the integral of pixel values on a horizontal line basis within a frame. Among multiple frames, the values of the line integral are normalized based on the average of the values of the line integral of associated horizontal lines. And based on that normalized a value of a line integral, flicker is analyzed.
Patent Document No. 2 discloses a technique for extracting information about the phase and amplitude of flicker based on a waveform representing the difference between the respective integral values in the same region of two images that have a flicker phase difference of 180 degrees between them.